An image sensor is a device that converts an optical image to an electric signal. It is used mostly in digital cameras and other imaging devices. Current image sensors are typically, for example, a charge-coupled device (CCD) or a complementary metal-oxide-semiconductor (CMOS) active-pixel sensor cell. In a CMOS active-pixel sensor cell, circuitry is needed next to each photo sensor (diode) to convert the light energy to a voltage. Additional circuitry on the chip is also included to convert the voltage to digital data. The circuitry receives power from Vdd through a switched rail line Vdd.
In many applications, though, electrons on the photodiode have a tendency to drift, reaching other structures on the cell. For example, electrons can drift to the floating diffusion, which can degrade the picture quality. Picture quality degradation due to carrier drift from the photo diode to other parts of the cell is especially important in global shutter mode imaging. Electron shielding, though, is a difficult challenge, since total shielding efficiencies may be needed on the order of 3,000,000 to one.
Accordingly, there exists a need in the art to overcome the deficiencies and limitations described hereinabove.